1. Field of the Invention
The present invention relates to a composition useful for applications as intumescent coatings. More particularly, the present invention relates to intumescent coatings. More particularly, the present invention relates to intumescent coatings which contain 4,4'-dinitrosulfanilide as the intumescent producing component.
2. Background of the Invention
Many types of intumescent coatings are known which swell or enlarge when heated. A variety of different substrates can be conveniently protected from heat and/or fire by these coatings.
Generally, intumescent coating compositions are formulated from a combination of a variety of constituents which enter into a complex series of reactions when intumesced by heat or fire. Many common compositions contain diammonium phosphate, ammonium phosphate or monoammonium phosphate as catalysts which function by acting as dehydrating acid derivatives, which react with a carbon containing material such as starch or pentaerythritol. The intumescent composition must also contain a resin component such as melamine formaldehyde to act as a binder for the various ingredients. The compositions generally are provided with special blowing agents which release gases for the swelling or foaming action of the coating at the proper decomposition temperature. It is apparent since the intumescent coatings generally contain a variety of constituents, that the sequence of reactions which takes place is dependent on the decomposition temperature of each ingredient which must possess environmental stability in order to function at the proper temperature. The principal problem with the ammonium phosphate containing compositions is that they are sensitive to water in that when water is present it interacts with water soluble components from the composition and therefore adversely affects the intumescent process. Consequently, a low density-swelled char having insulative characteristics cannot be obtained.
Another class of intumescent compositions is formulated upon the bisulfate salts of nitroaniline isomers as the principal ingredient in a binder matrix such as nitrocellulose. Such compositions are disclosed in U.S. Pat. No. 3,843,526. These compositions when applied as a coating produce voluminous chars which can insulate confined areas acting as a void filler. Another similar type of composition is one which contains the bisulfate salt of nitroaniline with a nitrile phenolic binder. With this composition a controlled char with insulating characteristics relative to the substrate can be obtained. However, these types of intumescent compositions, as well as other compositions, suffer deterioration from the environment.
Still another type of intumescent coating is one formulated from a combination of the ammonium salt of 1,4-nitroaniline-2-sulfonic acid and an epoxy-polysulfide copolymer. This composition provides thermal protection to heat sensitive articles such as ordnance with somewhat improved environmental stability.
The chief disadvantage of the intumescent compositions which contain the bisulfate salt of nitroaniline and the ammonium salt of 4-nitroaniline-2-sulfonic acid is that these components intumesce at high temperatures, and in the case of bisulfate salt, the corresponding compositions are not resistant to the environment. On the other hand, however, the ammonium salt of 1,4-nitroaniline-2-sulfonic acid is humidity resistant, but will leach from an applied composition when exposed to direct contact with water.
Another type of intumescent composition as disclosed in U.S. Pat. No. 3,912,845 is formulated from a combination of an amine-aldehyde interpolymer, wherein the amine component is an aminobenzenesulfonamide, with other adjuncts such as plasticizers, stabilizers, dispersing agents, pigments and the like. The intumescent composition disclosed in this patent would have limited long term environmental stability resulting from the free amino groups present within the intumescent compound. Free amino groups also could cause corrosion to metal substrates resulting in poor abhesion.
A need, therefore, continues to exist for an improved intumescent composition which is stable to the environment which intumesces at favorable temperatures and which does not contain water soluble components which can be leached from the composition when subjected to water.